Plot: Load all data before drawing a plot

Load all table data first, before drawing a plot. Otherwise the plot
might be incomplete because not all data is loaded yet due to partial
table loading.

See issue #499.

src/MainWindow.cpp

@@ -1682,6 +1682,10 @@ void MainWindow::updatePlot(SqliteTableModel *model, bool update)
 
         if(model)
         {
+            // Make sure all data is loaded before trying to plot anything
+            while(model->canFetchMore())
+                model->fetchMore();
+
             for(int i = 0; i < model->columnCount(); ++i)
             {
                 QVariant::Type columntype = guessdatatype(model, i);